This is used when you want to position the exposed form in the sidebar or anywhere else, but not with the view. Instead, a block will be made available to the Drupal block administration system, and the exposed form will appear there. Note that this block must be enabled manually, Views will not enable it for you.
To do this select "Exposed form in block: Yes" and choose one option from "Exposed form style".

Basic

When you expose a form and the view is loaded, no filter is selected and all items will displayed.

Input required

When you expose a form and the view is loaded, only the filter settings are shown. After you select one filter and hit the apply button, the items willi be shown.

You have several options to customize the appearance of the exposed forms:

Submit button text

Text to display in the submit button of the exposed form.

Include reset button

If checked the exposed form will provide a button to reset all the applied exposed filters